Timing stroke: A review on stroke pathophysiology and its influence over time on diffusion measures.

Diffusion imaging (DWI) is considered an optimal technique to detect hyperacute cerebral ischemia and has thus enriched the clinical management of patients with suspected stroke. Researchers have taken this technique beyond with Diffusion Tensor Imaging (DTI)-extracted measures, which have been proposed as biomarkers of stroke progression. A large body of literature report on the correlates between pathophysiological events, such as cytotoxic and vasogenic edema, and diffusion changes in the brain. However, a unified picture of these changes, and their exploration as stroke pathology progression biomarkers, remains to be done. We present here a narrative review on the different pathophysiological events underlying stroke from onset until late subacute stages and its relation to different brain edema forms. Studies included in this review used either DWI and/or DTI analysis in hyperacute (<24 h), acute (1-7 days), early subacute (7-30 days) and/or late subacute (1-6 months) phase of stroke, including human and animal models. Our conclusions are that diffusion measures should be considered as a potential proxy measure for stroke neuroinflammation status, specially in early stages of the disease. Furthermore, we suggest that the choice of diffusion measures and the interpretation of their changes, in both research and clinical settings, need to be linked to the different stroke phases to account correctly for the progression, and eventual resolution, of neuroinflammation.